U.S. Pat. No. 4,836,263 discloses an automotive screen device for shielding light in which spring means applies a biasing force to a roll having a light shielding screen wound thereon in a direction to wind up the roll, and an electric actuator or a hydraulic actuator applies an extending force to the light shielding screen via rotatable arms.
In this case, because the rotative force applied to the roll and the tension applied to the light shielding screen are not properly coordinated with each other, if either one of them is lost, the light shielding screen may be subjected to an excessive tension or may produce a slack. Furthermore, if the rotational angles of the rotary arms do not synchronize with each other, uneven tension may be applied to the screen and the screen may be creased or the smooth movement of the screen may become impossible. Therefore, mechanical means is required for synchronizing the rotary motions of the two arms, and this tends to complicate the structure.
In the case of a drive unit using an electric motor, the stop control of the motor is carried out by monitoring the electric current of the electric motor when the driven member has reached an end of the stroke of its movement. As this involves the detection of an over-current as a signal for stopping the electric motor, circuits for comparing and computing electric current levels are required, and the control device tends to be undesirably expensive. Furthermore, an over-current condition is necessarily produced immediately before stopping the electric motor, and this may reduce the durability of the electric motor.
In view of such problems of the prior art, a primary object of the present invention is to provide a blind device which can be stop controlled independently from the load of the electric motor, and which can prevent any excessive tension from being applied to the screen or any creases from being produced in the screen with a simple structure.